Cusp relation for the Pauli potential

In orbital-free density functional theory, only a Schr&ouml;dinger-like equation has to be solved for the square root of the electron density. In this equation, however, there is an extra potential in addition to the Kohn-Sham potential, the so-called Pauli potential. Cusp relations are now presented for this Pauli potential for spherically symmetric systems.</p

Flexibility of the quasi-non-uniform exchange-correlation approximation

In our previous study [Phys. Rev. B 86, 201104 (2012).] we introduced the so-called quasi-non-uniform gradient-level exchange-correlation approximation (QNA) and demonstrated its strength in producing highly accurate equilibrium volumes for metals and their alloys within density-functional theory. In this paper we extend the scheme to include the accuracy of the bulk modulus as an additional figure of merit and show that this scheme is flexible enough to allow the computation of accurate equilibrium volumes and bulk moduli at the same time. The power and feasibility of this scheme is demonstrated on NiAl and FeV binary alloys.</p

Space partitioning of exchange-correlation functionals with the projector augmented-wave method

We implement a Becke fuzzy cells type space partitioning scheme for the purposes of exchange-correlation within the GPAW projector augmented-wave method based density functional theory code. Space partitioning is needed in the situation where one needs to treat different parts of a combined system with different exchange-correlation functionals. For example, bulk and surface regions of a system could be treated with functionals that are specifically designed to capture the distinct physics of those regions. Here, we use the space partitioning scheme to implement the quasi-nonuniform exchange-correlation scheme, which is a useful practical approach for calculating metallic alloys on the generalized gradient approximation level. We also confirm the correctness of our implementation with a set of test calculations. Published under license by AIP Publishing

Alternative to the Kohn-Sham equations: The Pauli potential differential equation

A recently developed theoretical framework of performing self-consistent orbital-free (OF) density functional theory (DFT) calculations at Kohn-Sham DFT level accuracy is tested in practice. The framework is valid for spherically symmetric systems. Numerical results for the Beryllium atom are presented and compared to accurate Kohn-Sham data. These calculations make use of a differential equation that we have developed for the so called Pauli potential, a key quantity in OF-DFT. The Pauli potential differential equation and the OF Euler equation form a system of two coupled differential equations, which have to be solved simultaneously within the DFT self-consistent loop.</p

Density functional theory description of random Cu-Au alloys

Density functional alloy theory is used to accurately describe the three core effects controlling the thermodynamics of random Cu-Au alloys. These three core effects are exchange correlation (XC), local lattice relaxations (LLRs), and short-range order (SRO). Within the real-space grid-based projector augmented-wave (GPAW) method based on density functional theory (DFT), we adopt the quasinonuniform XC approximation (QNA), and take into account the LLR and the SRO effects. Our approach allows us to study the importance of all three core effects in a unified way within one DFT code. The results demonstrate the importance of the LLR term and show that going from the classical gradient level approximations to QNA leads to accurate formation energies at various degrees of ordering. The order-disorder transition temperatures for the 25%, 50%, and 75% alloys reach quantitative agreement with the experimental values only when also the SRO effects are considered

Formation and destabilization of Ga interstitials in GaAsN: Experiment and theory

Using first-principles total energy calculations we have found complex defects induced by N incorporation in GaAsN. The formation energy of the Ga interstitial atom is very significantly decreased due to local effects within the defect complex. The stability of the Ga interstitials is further increased at surfaces. The present results suggest that the energetically favorable Ga interstitial atoms are much more abundant in GaAsN than the previously considered N defects, which have relatively large formation energies. Our synchrotron radiation core-level photoemission measurements support the computational results. The formation of harmful Ga interstitials should be reduced by incorporating large group IV B atoms in GaAsN

Electron localization function implementation in the exact muffin-tin orbitals method

We report implementation of the electron localization function (ELF) within the exact muffin-tin orbitals (EMTO) formalism. The ELF is often used to study the nature of electronic bonding in different types of materials, and it is also an important ingredient in meta-generalized gradient approximations, which are one of the classes of exchange-correlation functionals. The correctness of the ELF implementation is verified with test calculations and comparison with previous literature results. The implementation supports not only regular ordered systems but also disordered systems that have been calculated using the coherent potential approximation method

Space partitioning of exchange-correlation functionals with the projector augmented-wave method

We implement a Becke fuzzy cells type space partitioning scheme for the purposes of exchange-correlation within the GPAW projector augmented-wave method based density functional theory code. Space partitioning is needed in the situation where one needs to treat different parts of a combined system with different exchange-correlation functionals. For example, bulk and surface regions of a system could be treated with functionals that are specifically designed to capture the distinct physics of those regions. Here, we use the space partitioning scheme to implement the quasi-nonuniform exchange-correlation scheme, which is a useful practical approach for calculating metallic alloys on the generalized gradient approximation level. We also confirm the correctness of our implementation with a set of test calculations.peerReviewe